JP2018079542A - Motor hand with force sensor and method for control thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suitably grip an object in a short time even if there is no information concerning a shape, a weight and a contact resistance of a surface of an object to be gripped.SOLUTION: A hardness of an object can be determined by providing a force sensor to a gripping part which grips the object, a force sensor value detected by the force sensor, an encoder value which can be detected by a travel quantity of a drive part moved by a position control part, and an additional torque value which can be detected from a force applied onto the drive part by a force control part are recorded by performing a clamping operation, and whether the object is gripped when moving a motor hand is confirmed by an external sensor such as a photo-electric switch or the like. If the object is not gripped, fastening of a constant quantity is performed again, the motor hand is moved, and whether the object is gripped is confirmed. This process is repeated until the object can be suitably gripped, thereby setting an optimal gripping force.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a motor hand provided with a force sensor for detecting a gripping force by opening and closing a gripping portion by an actuator and detecting a gripping force, and a control method thereof.

  Several proposals for a motor hand with a force sensor have been made, and Patent Document 1 discloses that a force sensor is provided in a finger portion for gripping an object to stably and accurately detect a gripping force over a wide range. Is possible. When the force applied to the finger part is detected by the force sensor when the finger part comes into contact with the object and it is determined that the force detection value exceeds the set force contact value, the position feedback control is switched to the force feedback control. An electric hand that can grip an object with an accurate gripping force by driving an actuator so that a force detection value matches a set force target value by force feedback control is described.

  Patent Document 2 includes a force detection unit that detects a force applied to an end effector having a first finger unit and a second finger unit, provided at the tip of an arm provided in a robot body. When the first finger part and the second finger part are brought close to each other based on the force detected by the above and the first finger part comes into contact with the grasped object, the arm is held in the first state while keeping the contacted state. Move in the direction in which the finger is provided. Thereby, the center of the hand and the center position of the workpiece can be brought closer without the information on the shape of the object. As a result, there is described a robot that can appropriately hold an object in a short time.

JP 2014-108466 A JP2015-85455

  The basic operation of the hand is to grip and carry the object, and a hand having a structure in which the object is sandwiched between a plurality of gripping units is generally used. When trying to transport a fragile or light object such as glass, or a hard or heavy object such as iron with a common hand, it is necessary to adjust the gripping force for each object. It cannot automatically deal with objects.

  To grip different objects, it is necessary to set the clamping position, gripping force, and hardness for each object. Depending on the shape, weight, and surface contact resistance (friction resistance) of the object, There is a problem that it takes time and difficulty to set an optimal force threshold and the like.

  In the invention described in Patent Document 1, in order to grasp an object, the force detection value detected by the force sensor can be matched with a set force target value. In this case, it is necessary to set the target value of the force for gripping the object in advance, and it takes time to find the optimal target value of the force by examining the shape, weight, and surface contact resistance of the object. There's a problem.

  In the invention described in Patent Document 2, even if there is no information related to the shape of the object, the center of the hand and the center position of the workpiece can be brought close to each other and the object can be appropriately gripped in a short time. The gripping end condition is that the gripping force of the hand at this time is equal to or greater than a predetermined value set in advance. Therefore, it is necessary to set an appropriate gripping force for gripping the object, and there is a problem that it takes time to obtain an optimal gripping force setting value corresponding to the object as described above.

  Therefore, the present invention provides a motor hand and a control method for the motor hand that can appropriately grasp the object in a short time without the information on the shape, weight, and strength of the object.

  The present invention relates to a motor hand that grips an object by opening and closing a gripping portion, the force detection portion that is provided in the gripping portion and detects a force acting in the opening and closing direction of the gripping portion, and the gripping portion. A motor hand comprising: an actuator to be driven; a drive unit that drives the actuator; a position control unit that controls a position of the drive unit; and a force control unit that controls the force of the drive unit.

  The force detection unit is at least one force sensor provided in the gripping unit, and by performing a clamping operation, a force sensor value from the force sensor that is the force detection unit and a drive moved by the position control unit It is possible to detect the additional torque value from the encoder value from the movement amount of the part and the force applied to the drive part by the force control part. Each value is recorded, and it is confirmed that an external sensor such as a photoelectric switch holds the object when the motor hand is moved. If it is not gripped, increase the additional torque value again, tighten a certain amount, move the motor hand to check whether the target is gripped, and grip the target with the grip Each value is increased until the value becomes, and this step is repeated until the object can be properly gripped, thereby setting a value that allows proper gripping. As a result, when grasping different objects, the object can be grasped appropriately in a short time without knowing the shape, weight, contact resistance, etc. of the object.

  As described above, according to the present invention, when a plurality of objects are transported with a common hand, the object can be appropriately obtained in a short time even when there is no information on the shape, weight, or strength of the object. It is possible to provide a motor hand and a control method thereof.

It is a schematic block diagram explaining an example of the motor hand with a force sensor of this invention. It is a block diagram of embodiment of this invention. It is a transition diagram of values that can be detected by the present invention. It is a flowchart regarding embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic diagram illustrating an example of a motor hand with a force sensor according to the present invention. The motor hand 1 has two open / close gripping portions 10. The actuator 12 is a drive mechanism comprising a motor (not shown), a timing belt, a trapezoidal screw, a trapezoidal nut, and a linear guide. The rotation of the motor is decelerated by the timing belt, and converted into a linear motion by the trapezoidal screw, trapezoidal nut, and linear guide. It is.

  The actuator 12 moves in a straight line by the actuator 12 to open and close, and the force sensor 11 is installed in the grip 10. The force sensor 11 detects the force sensor value. An arrow 15 represents an operation direction of the gripping unit 10 and grips the target object 2 by opening and closing.

  The position control unit 13 is an encoder that detects the amount of movement of the actuator 11. The encoder value is detected by detecting the rotation angle of the motor.

  The force control unit 14 is a controller that controls the motor hand 1. Based on the grip command from the force control unit 14, the gripping operation of the object 2 according to the present invention is executed. An additional torque value transmitted from the motor is detected by an amplifier built in the force control unit 14.

  In FIG. 1, two force sensors 11 are installed in the gripping unit 10, but when the gripping force of the same magnitude is applied to the two gripping units 10, the force sensor 11 may be one. . In addition, since the gripping unit 10 is installed so as to sandwich the object symmetrically, the number of the gripping units 10 is two. However, if the gripping force of the same magnitude is applied, but the number of gripping units is three. You may increase to four. Other mechanisms may be used as long as the rotation of the motor is converted into the linear guide linear motion.

  FIG. 2 is a configuration diagram of an embodiment of the present invention. The actuator 32 grips the object by opening and closing the grip portion 30. The force when the grip unit 30 comes into contact with the object is a force sensor value detected by the force detection unit 31, and the amount of movement of the grip unit 30 is an encoder value detected by the position control unit 33. The actuator 32 incorporates a motor (not shown) and is driven by the drive unit 34. The drive unit 34 is an amplifier with a built-in controller that is the force control unit 35, and detects an additional torque value as a gripping force applied to the object by the gripping unit.

  FIG. 3 is a transition diagram of values that can be detected by the present invention. T01 represents the start of the gripping operation of the motor hand, T02 represents the time when the object is touched by the opening / closing operation of the motor hand, and T03 represents the time when the gripping of the motor hand is completed.

  The additional torque value that can be detected from the force control unit is a constant value until T02 after applying a large amount of force corresponding to the initial resistance at T01. After reaching T02, the value is gradually increased until reaching T03, and after T03, the value is constant.

  The encoder value that can be detected from the position control unit increases with a constant transition from T01 according to the additional torque value. After reaching T02, the encoder value is slightly increased by the amount that the object is tightened. It is constant to maintain.

  The force sensor value that can be detected from the force detector is not detected from T01 to T02 because it is not in contact with the object. From T02 to T03, it rises sharply when it is hard and gradually rises when it is soft. After T03, it becomes constant in order to maintain the gripping state.

  FIG. 4 is a flowchart of an embodiment of the present invention. When the grip command is started, the motor hand moves to a position where the object can be gripped. After the movement, force control is started, the motor is driven, position control is performed, and the gripper is opened and closed until it comes into contact with the object. When the object is touched, the force detection unit detects the force sensor value, determines the hardness of the object from the transition of the increase in the force sensor value, and determines the target value of the additional torque value to be applied. When the target value is reached, move the hand. At this time, an external sensor such as a photoelectric switch is used to check whether the object is being gripped. When not gripping, the force sensor value at the time of gripping failure is stored, and the gripping operation is performed again with a value larger than that value. This is repeated until the gripping operation is successful. When the object has been successfully gripped, if the number of successes is less than 3, the gripping operation is started again with the same force sensor value. When the number of successful grips reaches 3, the threshold values of the additional torque value, encoder value, and force sensor value at that time are stored, the process returns to the initial position, and the operation for the grip command is terminated. In this example, the number of successful grips is three, but the number of successes may be arbitrarily changed.

Hereinafter, each step will be described.
[S01] In accordance with the grip command, the movement of the motor hand is started to the designated position.
[S02] A gripping operation is started to drive the motor.
[S03] As the motor is driven, the gripper is moved until it contacts the object.
[S04] The force sensor value detects whether the gripping part has contacted the symmetrical part.
[S05] It is determined whether the amount of increase in the force sensor value during tightening of the object is moderate. If it is gradual (YES), the process proceeds to S06, and if not gradual (NO), the process proceeds to S07.
[S06] The object is determined to be soft, and the additional torque value is set to a small value. In the second and subsequent times, the value is larger than the previously stored value. The amount of change at this time is small.
[S07] The object is determined to be hard, and the value of the additional torque value is increased. In the second and subsequent times, the value is larger than the previously stored value. The amount of change at this time is large.
[S08] A lifting operation is performed while holding the object.
[S09] The external sensor checks whether the motor hand after the lifting operation is holding the object. If it is not gripped (NO), the process proceeds to S10, and if it is gripped (YES), the process proceeds to S11.
[S10] The force sensor value at the time of gripping failure is stored, and the gripping operation is restarted from the beginning.
[S11] The number of successful grips is stored, and it is checked whether the number of successes is three. If less than three times (NO), the object is returned to the original position, and the gripping operation is started again. In the case of three times (YES), the object is returned to the original position, the threshold values of the additional torque value, encoder value, and force sensor value are stored, the hand is returned to the initial position, and the operation is terminated.

DESCRIPTION OF SYMBOLS 1 Motor hand 2 Object 10 Gripping part 11 Force sensor 12 Actuator 13 Position control part 14 Force control part 15 Movable direction

30 Gripping part 31 Force detection part 32 Actuator 33 Position control part 34 Drive part 35 Force control part

Claims (3)

  In a motor hand having at least two gripping portions that grips an object by an opening / closing operation, a force detection portion that is provided on the gripping portion and detects a force acting in an opening / closing direction of the gripping portion, and drives the gripping portion A force sensor-equipped motor hand comprising: an actuator for driving, a drive unit for driving the actuator, a position control unit for controlling the position of the drive unit, and a force control unit for controlling the force of the drive unit.   The motor hand according to claim 1, wherein the force detection unit is at least one force sensor provided in the grip unit. 3. The motor hand according to claim 1, wherein the object is obtained from a force sensor value that can be detected from the force detector, an encoder value that can be detected from the position control unit, and an additional torque value that can be detected from the force control unit. A method for controlling a motor hand with a force sensor, comprising: a step of determining the hardness of the object; and a step of determining whether the value is such that the object can be gripped.